The disclosure of Japanese Patent Application No. 2000-301323 filed on Sep. 29, 2000 including the specification, drawings and abstract are incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a measuring method for measuring the eccentricity or diameter of a work portion (i.e., a portion undergoing machining) of a workpiece, which portion is provided eccentrically with respect to the rotation center of the workpiece and has a circular cross section, as well as to a machining method capable of correcting a machining program on the basis of the measured eccentricity or diameter.
2. Description of the Related Art
When a workpiece is machined by use of a machine tool, the machining of the workpiece is sometimes effected, while the dimension or the like of the workpiece is measured by use of a measurement unit mounted on the machine tool. In particular, when a crankpin of a crankshaft serving as a workpiece is ground while the crankshaft is rotated about the journals of the crankshaft, a following-type size-measurement unit produced by, for example, Marposs S.P.A. (Italy) is typically used for measuring the diameter of the crankpin, which revolves about the journals. Such a following-type size-measurement unit is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 2000-127038.
The following-type size-measurement unit will be described with reference to FIG. 10. FIG. 10 shows a case in which the radius of a crankpin 108 ground on a cylindrical grinder 100 which has a grinding wheel 101 is measured by use of a following-type size-measurement unit 103. The following-type size-measurement unit 103 is attached to a support member 104 mounted on a wheel head 102 of the cylindrical grinder 100 in such a manner that the size-measurement unit 103 is swingable about a rotary shaft 105. The size-measurement unit 103 can be moved from a standby position indicated by an alternate long and two short dashes line in FIG. 10 to a position indicated by a solid line in FIG. 10 at which the size-measurement unit 103 measures the size of the revolving crankpin 108.
The measurement head of the size-measurement unit 103 has a V-block 106. A probe 107 is supported by a shaft passing through the center of a V-groove portion of the V-block 106 and is urged forward by an unillustrated spring in such a manner that the probe 107 can be retreated. The amount of axial movement of the probe 107 is detected electrically, and an electrical signal corresponding thereto is output from the measurement head.
When the crankpin 108 is to be measured, as indicated by the solid line, the V-block 106 is brought into contact with the outer circumference of the crankpin 108, so that the crankpin 108 comes into contact with the V-block 106 at two locations. At this time, the probe 107 comes into contact with the outer circumference of the crankpin 108 due to the restoration force of the unillustrated spring. Subsequently, the radius of the crankpin 108 is obtained from the geometric shape of the V-block 106 and the position of the probe 107 in contact with the crankpin 108, which is in contact with the V-block 106.
However, the conventional following-type size-measurement unit is expensive.
Further, since only the radius of a work portion can be measured, the diameter of the work portion must be calculated from the measured radius. In this case, a greater error is produced as compared with the case in which the diameter of the work portion is measured directly.
Moreover, the size of the V-groove portion of the V-block 106 and the swing support mechanism employed for supporting the V-block 106 impose limitations on the measurable workpiece diameter and measurable crankshafts, resulting in a narrow measurement range.
In view of the foregoing, an object of the present invention is to provide a measuring method which accurately measures the eccentricity and/or diameter of a work portion within a widened range at low cost.
Another object of the present invention is to provide a machining method capable of correcting a machining program on the basis of the eccentricity and/or diameter measured by the measuring method.
The present invention provides a work-portion measuring method for measuring a diameter of a cylindrical work portion of a workpiece mounted on a machine tool, the work portion being concentric with a rotation center of the workpiece, the method comprising the steps of: setting a first distance between a rotation center of the workpiece and a reference point provided on the machine tool; measuring a second distance between the reference point and an outer circumferential surface of the work portion; and obtaining the diameter of the work portion on the basis of the first and second distances.
The present invention provides a machining method for machining an outer circumferential surface of a cylindrical work portion of a workpiece in accordance with a machining program, the work portion being concentric with a rotation center of the workpiece, the method comprising the steps of: measuring a diameter of the work portion by the above-described work-portion measuring method; correcting the machining program based on the measured diameter of the work portion; and machining the outer circumferential surface of the work portion in accordance with the corrected machining program.
The present invention provides another work-portion measuring method for measuring a diameter and eccentricity of a cylindrical work portion of a workpiece mounted on a machine tool, the work portion being eccentric with respect to a rotation center of the workpiece, the method comprising the steps of: setting a first distance between a rotation center of the workpiece and a reference point provided on the machine tool; measuring a second distance between the reference point and an innermost point on an outer circumferential surface of the work portion; measuring a third distance between the reference point and an outermost point on the outer circumferential surface of the work portion; and obtaining the diameter and eccentricity of the work portion on the basis of the first, second, and third distances.
The present invention provides a machining method for machining an outer circumferential surface of a cylindrical work portion of a workpiece in accordance with a machining program, the work portion being eccentric with a rotation center of the workpiece, the method comprising the steps of: measuring a diameter and eccentricity of the work portion by the above-described work-portion measuring method; correcting the machining program based on the measured diameter and eccentricity of the work portion; and machining the outer circumferential surface of the work portion in accordance with the corrected machining program.
In the measuring method of the present invention, since the diameter and/or eccentricity is measured on the basis of distances, a measurement apparatus used in the method is required to detect distance only. Therefore, a contact-type measurement apparatus or any other simple measurement apparatus can be used in order to reduce cost. In addition, the measuring method of the present invention provides higher measurement accuracy as compared with conventional measuring methods.
In the machining methods of the present invention, since the machining program is corrected on the basis of the measured diameter and/or eccentricity of the work portion, the work portion can be finished to higher accuracy.
The machining methods of the present invention preferably comprise an additional step of comparing the measured diameter or eccentricity of the work portion with a tolerance in order to judge whether the work portion is good. In this case, properness of machining can be judged easily on the machine.